1. Field of the Invention
The invention relates to the control of emission from a laser. It is potentially useful in many fields including use as transducers in communication systems, laser oscillators, optical transistors, and optical monostable or bi-stable devices.
2. Description of Related Art
The use of lasers in many applications has recently increased dramatically. For example, the use of semiconductor laser diodes for optical communication systems has increased over the past two decades due primarily to their small size, high efficiency, and susceptibility to high speed modulation. See K.Y. Lau and A. Yariv, "Ultra-High Speed Semiconductor Lasers", IEEE J. Quan. Elec. QE-21, pages 121-138, Feb. 1985. Currently, they are used in fiber-optic systems, opto-electronic integrated circuits (OEICs), and free-space laser communications.
In the communications field, the need for transmission of data at increasingly higher data rates has driven the development of high-speed optical communication systems. Because of their small size, high efficiency, and fast response time, semiconductor lasers have come to be used extensively as a source of light in ground-based optical communication systems.
In satellite systems, the use of optical transceivers employing laser diodes is even more attractive. In addition to the potential of high data rates, these systems are compact, long lived, and are relatively insensitive to external interference.
Future systems designated for higher data rates and greater range will require higher power lasers with tight control on the beam quality (i.e., a highly coherent, nearly diffraction-limited beam). Increasing the power output of phased-array laser diodes will require an increase in the number of stripes in the array. Unfortunately, the addition of more stripes in a laser array increases the current necessary to operate the laser as well as increasing the device capacitance.
At high data rates (into the multi-gigahertz range) it becomes extremely difficult to vary the laser output. The most common method of modulating the output of these lasers (for low to moderate frequencies) is by direct current modulation. However, as modulation rates increase (past a few gigahertz) and operating currents increase (e.g., in phased array lasers), problems associated with the dynamics of current modulation of the laser have necessitated the development of other methods. These methods usually include guiding the emitted light through external waveguide(s) in which the optical properties of the waveguide material may be varied by application of a bias. This variation consists of a change in the optical absorption and/or change in the optical index of refraction.
Unfortunately, while acceptable in some applications, these methods have not (to date) proven useful for modulating high-power phased-array diode lasers. This is due primarily to the inherent optical absorption (even in the "clear" or "bleached" state) and distortion experienced by a wavefront passing through waveguides fabricated with currently available techniques and materials.
One method of modulating high power phased arrays is to use the array as an amplifier for a smaller, well-behaved master oscillator (known as the MOPA or master oscillator-power amplifier configuration). See M.K. Chun, L. Goldberg and J.F. Weller, "Injection-Beam Parameter Optimization of an Injection-Locked Diode-Laser Array", Opt. Lett., Vol. 14, No. 5, pages 272-274, March 1989. While this method has shown promising results, instabilities in the beam quality and wavelength ("chirp") of the master oscillator at high modulation frequencies may ultimately limit the usefulness of this method of modulation.
Quenching of the output from a single laser by injection of light from another completely separate laser has been observed in the past for GaAs diode lasers and other systems. See, U.S. Pat. No. 3,431,437 to W.F. Kosonocky, entitled "Optical System for Performing Digital Logic", issued Mar. 4, 1969; Alan B. Fowler, "Quenching of Gallium-Arsenide Injection Lasers", Appl. Phys. Lett., Vol. 3, No. 1, pages 1-3, July 1963; G.J. Lasher and A.B. Fowler, "Mutually Quenched Injection Lasers as Bistable Devices", IBM J. of Res. and Dev., Vol 8, No. 4, pages 471-475, Sept. 1964; J.L. Fitz, W.T. Beard, C.W. Lowry, S. Ovadia and C.H. Lee, "5.0-GHz Modulation Rate of Light by Light in GaAs Laser Diode", presented at CLEO, Jun. 13, 1986, paper FH2; W.J. Grande and C.L. Tang, "Semiconductor Laser Logic Gate Suitable for Monolithic Integration", Appl. Phys. Lett., Vol. 51, No. 22, pages 1780-1782, July 1987; John L. Fitz, "Optical Logic via Optically Controlled Lasers", Applied Physics Projects report written for a class at Johns Hopkins University, Jul. 9, 1988.
It is also known that there is a certain amount of transverse stimulated emission inherently present within a linear phased-array laser. See, D.R. Scifres, R.D. Burnham, C. Lindstrom, W. Streifer, and T.L. Paoli, "Phase-Locked (GaAl)As Laser Emitting 1.5 W cw per Mirror", Appl. Phys. Lett., Vol. 42, No. 8, pages 645-647, Jan. 1983; D.R. Scifres, C. Lindstrom, R.D. Burnham, W. Streifer, and T.L. Paoli, "Phase-Locked (GaAl)As Laser Diode Emitting 2.6 W cw from a Single Mirror", Elec. Lett., Vol. 19, No. 5, pages 169-171, March 1983; G.L. Harnagel, P.S. Cross, D.R. Scifres, D.F. Welch, C.R. Lennon, and D.P. Worland, "High-Power Quasi-cw Monolithic Laser Diode Linear Arrays", Appl. Phys. Lett., Vol. 49, No. 21, pages 1418-19, Nov. 1986; R.C. Goodfellow, A.C. Carter, G.J. Rees, and R. Davis, "Radiance Saturation in Small-Area GaInAsP/InP and GaAlAs/GaAs LED's, IEEE Trans. on Elec. Dev. ED-28(4), pages 365-371, 1981.